Rubber composition

ABSTRACT

A rubber composition having an adhesion to a composition based on natural rubber, the composition being at least based on 5 to 95 phr of polyisoprene comprising a content by weight of 1,4-cis bonds of at least 90% of the weight of the polyisoprene; 5 to 95 phr of copolymer of ethylene and of a 1,3-diene of formula CH2═CR—CH═CH2, the ethylene units in the copolymer representing more than 50 mol % of the monomer units of the copolymer, the symbol R representing a hydrocarbon chain having 3 to 20 carbon atoms; and a crosslinking system. Also disclosed is a tire, in particular a tire provided with a sidewall, comprising this composition.

The field of the present invention is that of rubber compositionscomprising a highly saturated diene elastomer, in particularcompositions intended for use in a tyre, preferably in tyre sidewalls.

A tyre usually comprises two beads intended to come into contact with arim, a crown composed of at least one crown reinforcement and a tread,and two sidewalls, the tyre being reinforced by a carcass reinforcementanchored in the two beads. A sidewall is an elastomer layer positionedoutside the carcass reinforcement relative to the internal cavity of thetyre, between the crown and the bead, so as to totally or partiallycover the region of the carcass reinforcement extending from the crownto the bead.

In the conventional manufacture of a tyre, the various constituentcomponents of the crown, of the carcass reinforcement, of the beads andof the sidewalls are assembled to form a pneumatic tyre. The assemblystep is followed by a step of forming the tyre so as to give theassembly the toric shape before the in-press curing step. As thesidewall of a tyre is subjected to cycles of deformation such as bendingduring rolling of the tyre, the rubber composition constituting asidewall of a tyre must be both sufficiently flexible and not veryhysteretic.

As the sidewall is also exposed to the action of the ozone, a rubbercomposition constituting a sidewall must have good ozone resistanceproperties. With a view to reducing the sensitivity of tyre sidewalls tothe ozone, it has been proposed in document EP 2 682 423 A1 to useelastomers which are copolymers of ethylene and of 1,3-diene.Nevertheless, there still remains the concern of further improving theproperties of the rubber compositions containing a diene copolymer whichis rich in ethylene, in particular a diene copolymer for which the molaramount of ethylene is greater than 50%.

Specifically, the sidewall must adhere to the layer on which it isplaced during the manufacture of the tyre. This layer is generally acarcass ply or an internal reinforcing rubber, the composition of whichgenerally comprises a diene elastomer matrix, generally consisting ofnatural rubber.

Consequently, it remains important that the composition of the sidewalladheres well to a diene composition, in particular to improve the holdof the cured interfaces, and therefore the service life of the tyre.

Continuing its research, the applicant has discovered that the use of acopolymer of ethylene and of a specific 1,3-diene makes it possible toimprove the adhesion of the composition to a diene composition.

Thus, a first subject of the invention is a rubber composition at leastbased on:

-   -   5 to 95 phr of polyisoprene comprising a content by weight of        1,4-cis bonds of at least 90% of the weight of the polyisoprene,    -   5 to 95 phr of copolymer of ethylene and of a 1,3-diene of        formula (I), the ethylene units in the copolymer representing        more than 50 mol % of the monomer units of the copolymer,        CH₂═CR—CH═CH₂ (I) the symbol R representing a hydrocarbon chain        having 3 to 20 carbon atoms, and    -   a crosslinking system.

Another object of the invention is a tyre comprising this composition.

I—DEFINITIONS

The expression “based on” used to define the constituents of a catalyticsystem or of a composition is understood to mean the mixture of theseconstituents, or the product of the reaction of a portion or of all ofthese constituents with one another.

The expression “composition based on” should be understood as meaning acomposition including the mixture and/or the product of the in situreaction of the various constituents used, some of these constituentsbeing able to react and/or being intended to react with each other, atleast partially, during the various phases of manufacture of thecomposition; the composition thus possibly being in the totally orpartially crosslinked state or in the non-crosslinked state.

Unless otherwise indicated, the contents of the units resulting from theinsertion of a monomer into a copolymer are expressed as molarpercentage with respect to all of the monomer units of the copolymer.

The expression “phr” should be understood as meaning, for the purposesof the present invention, the part by weight per hundred parts by weightof elastomer.

Unless explicitly indicated otherwise, in the present text allpercentages (%) indicated are percentages (%) by weight.

Furthermore, any interval of values denoted by the expression “between aand b” represents the range of values extending from more than a to lessthan b (i.e. limits a and b excluded), whereas any interval of valuesdenoted by the expression “from a to b” means the range of valuesextending from a up to b (i.e. including the strict limits a and b). Inthe present document, when an interval of values is denoted by theexpression “from a to b”, the interval represented by the expression“between a and b” is also and preferentially denoted.

When reference is made to a “predominant” compound, this is understoodto mean, for the purposes of the present invention, that this compoundis predominant among the compounds of the same type in the composition,that is to say that it is that which represents the greatest amount byweight among the compounds of the same type. Thus, for example, apredominant elastomer is the elastomer representing the greatest weightrelative to the total weight of the elastomers in the composition. Inthe same way, a “predominant” filler is that representing the greatestweight among the fillers of the composition. By way of example, in asystem comprising just one elastomer, the latter is predominant for thepurposes of the present invention and, in a system comprising twoelastomers, the predominant elastomer represents more than half of theweight of the elastomers. On the contrary, a “minor” compound is acompound which does not represent the greatest fraction by weight amongthe compounds of the same type. Preferably, the term “predominant” isintended to mean present at more than 50%, preferably more than 60%,70%, 80%, 90%, and more preferentially the “predominant” compoundrepresents 100%.

The carbon-comprising compounds mentioned in the description can be offossil or biobased origin. In the latter case, they can partially orcompletely result from biomass or be obtained from renewable startingmaterials resulting from biomass. Polymers, plasticizers, fillers, andthe like, are concerned in particular.

All the values for glass transition temperature “Tg” described in thepresent document are measured in a known way by DSC (DifferentialScanning calorimetry) according to Standard ASTM D3418 (1999).

II—DESCRIPTION OF THE INVENTION II-1 Elastomer Matrix

According to the invention, the composition comprises from 5 to 95 phrof copolymer of ethylene and of a 1,3-diene of formula (I), the ethyleneunits in the copolymer representing more than 50 mol % of the monomerunits of the copolymer,

CH2═CR—CH═CH2  (I)

the symbol R representing a hydrocarbon chain having 3 to 20 carbonatoms.

Preferably, the copolymer contains ethylene units which representbetween 50 mol % and 95 mol % of the monomer units of the copolymer,that is to say between 50 mol % and 95 mol % of the ethylene units andof the units of the 1,3-diene. Very preferably, the copolymer containsethylene units which represent from 60 mol % to 90 mol %, preferablyfrom 70 mol % to 85 mol %, of the monomer units of the copolymer.

The 1,3-diene of formula (I) is a substituted 1,3 diene, which can giverise to units of 1,2 configuration represented by formula (1), of 3,4configuration represented by formula (2) and of 1,4 configuration, thetrans form of which is represented below by formula (3).

As is also well known, the ethylene unit is a unit of —(CH₂—CH₂)—moiety.

The copolymer which is useful for the purposes of the invention is acopolymer of ethylene and of the 1,3-diene, which implies that themonomer units of the copolymer are units resulting from thepolymerization of ethylene and of the 1,3-diene. The copolymer thuscomprises ethylene units and units of the 1,3-diene. According to theinvention, the 1,3-diene can be just one compound, that is to say justone 1,3-diene of formula (I), or can be a mixture of 1,3-dienes offormula (I), the 1,3-dienes of the mixture differing from one another bythe group represented by the symbol R. The copolymer which is useful forthe purposes of the invention is advantageously a random copolymeraccording to any one of the embodiments of the invention.

According to a first variant of the invention, the copolymer containsunits of the 1,3-diene of 1,2 or 3,4 configuration which represent morethan 50 mol % of the units of the 1,3-diene. In other words, in thecopolymer the units of the 1,3-diene contain more than 50 mol % of theunits of 1,2 configuration or of 3,4 configuration. In this variant, thebalance to 100 mol % of the units of the 1,3-diene in the copolymer iscompletely or partially formed of units of the 1,3-diene of 1,4configuration. According to this first variant, preferentially more thanhalf of the units of the 1,3-diene of 1,4 configuration are of trans-1,4configuration, more preferentially all the units of the 1,3-diene of 1,4configuration are of trans-1,4 configuration.

According to a second variant of the invention, in the copolymer theunits of the 1,3-diene contain more than 50% of 1,4 configuration. Inother words, the units of the 1,3-diene of 1,4 configuration representmore than 50 mol % of the units of the 1,3-diene. In this variant, thebalance to 100 mol % of the units of the 1,3-diene in the copolymer iscompletely or partially formed of units of the 1,3-diene of 1,2 or 3,4configuration. Preferably, the units of the 1,3-diene of 1,4configuration represent more than 70 mol % of the units of the1,3-diene. Advantageously, more than half of the units of the 1,3-dieneof 1,4 configuration are of trans-1,4 configuration, which means thatthe units of the 1,3-diene of trans-1,4 configuration represent morethan 50 mol % of the units of the 1,3-diene of 1,4 configuration.

Whatever the abovementioned variant, in formula (I) of the 1,3-diene,the hydrocarbon chain represented by the symbol R can be an unsaturatedchain of from 3 to 20 carbon atoms. Preferably, the symbol R representsa hydrocarbon chain having from 6 to 16 carbon atoms. The hydrocarbonchain represented by the symbol R can be a saturated or unsaturatedchain. Preferably, the symbol R represents an aliphatic chain, in whichcase in formula (I) of the 1,3-diene, the hydrocarbon chain representedby the symbol R is an aliphatic hydrocarbon chain. It can be a linear orbranched chain, in which case the symbol R represents a linear orbranched chain. Preferably, the hydrocarbon chain is acyclic, in whichcase the symbol R represents an acyclic chain. Preferably, the symbol Rrepresents an unsaturated and branched acyclic hydrocarbon chain. Thehydrocarbon chain represented by the symbol R is advantageously anunsaturated and branched acyclic chain containing from 3 to 20 carbonatoms, in particular from 6 to 16 carbon atoms. Very advantageously, the1,3-diene is myrcene or β-farnesene.

According to a preferential embodiment of the invention, the 1,3-dieneis myrcene. According to another preferential embodiment of theinvention, the 1,3-diene is β-farnesene. Preferably, the copolymer ofethylene and of the 1,3-diene has a glass temperature below −35° C.,preferably between −90° C. and −35° C.

The copolymer may be prepared by a process which comprises thecopolymerization of ethylene and of the 1,3-diene in the presence of acatalytic system based at least on a metallocene of formula (II) and onan organomagnesium compound of formula (III)

P(Cp ¹Cp ²)Nd(BH₄)_((1+y))L_(y)-N_(x)  (II)

MgR¹R²  (III)

in which:

-   -   Cp¹ and Cp², which may be identical or different, being selected        from the group consisting of the cyclopentadienyl group of        formula C₅H₄, the unsubstituted fluorenyl group of formula C₁₃H₈        and substituted fluorenyl groups,    -   P being a group bridging the two Cp¹ and Cp² groups and        representing a ZR³R⁴ group, Z representing a silicon or carbon        atom, R³ and R⁴, which may be identical or different, each        representing an alkyl group comprising from 1 to 20 carbon        atoms, preferably a methyl,    -   y, which is an integer, being equal to or greater than 0,    -   x, which is or is not an integer, being equal to or greater than        0,    -   L representing an alkali metal selected from the group        consisting of lithium, sodium and potassium,    -   N representing a molecule of an ether, preferably diethyl ether        or tetrahydrofuran,    -   R¹ and R², which may be identical or different, representing a        carbon group.

Mention may be made, as substituted fluorenyl groups, of thosesubstituted by alkyl radicals having from 1 to 6 carbon atoms or by arylradicals having from 6 to 12 carbon atoms. The choice of the radicals isalso guided by the accessibility to the corresponding molecules, whichare the substituted fluorenes, because the latter are commerciallyavailable or can be easily synthesized.

Mention may more particularly be made, as substituted fluorenyl groups,of the 2,7-di(tert-butyl)fluorenyl and 3,6-di(tert-butyl)fluorenylgroups. The 2, 3, 6 and 7 positions respectively denote the position ofthe carbon atoms of the rings as represented in the scheme below, the 9position corresponding to the carbon atom to which the bridge P isattached.

The catalytic system can be prepared conventionally by a processanalogous to that described in patent application WO 2007054224 or WO2007054223. For example, the organomagnesium compound and themetallocene are reacted in a hydrocarbon solvent typically at atemperature ranging from 20° C. to 80° C. for a period of time ofbetween 5 and 60 minutes. The catalytic system is generally prepared inan aliphatic hydrocarbon solvent, such as methylcyclohexane, or anaromatic hydrocarbon solvent, such as toluene. Generally, after itssynthesis, the catalytic system is used in this form in the process forthe synthesis of the copolymer in accordance with the invention.

Alternatively, the catalytic system can be prepared by a processanalogous to that described in patent application WO 2017093654 A1 or inpatent application WO 2018020122 A1. According to this alternative, thecatalytic system further contains a preformation monomer selected from aconjugated diene, ethylene or a mixture of ethylene and a conjugateddiene, in which case the catalytic system is based at least on themetallocene, the organomagnesium compound and the preformation monomer.For example, the organomagnesium compound and the metallocene arereacted in a hydrocarbon solvent typically at a temperature of from 20°C. to 80° C. for 10 to 20 minutes in order to obtain a first reactionproduct, then the preformation monomer, selected from a conjugateddiene, ethylene or a mixture of ethylene and of a conjugated diene, isreacted with this first reaction product at a temperature ranging from40° C. to 90° C. for 1 h to 12 h. The conjugated diene, as preformationmonomer, is preferably a 1,3-diene such as 1,3-butadiene, isoprene orelse a 1,3-diene of formula (I), in particular myrcene or β-farnesene.The catalytic system thus obtained can be used immediately in theprocess in accordance with the invention or be stored under an inertatmosphere before it is used in the process in accordance with theinvention.

The metallocene used for preparing the catalytic system can be in theform of a crystalline or non-crystalline powder, or else in the form ofsingle crystals. The metallocene can be provided in a monomer or dimerform, these forms depending on the method of preparation of themetallocene, as for example is described in patent application WO2007054224 or WO 2007054223. The metallocene can be preparedconventionally by a process analogous to that described in patentapplication WO 2007054224 or WO 2007054223, in particular by reaction,under inert and anhydrous conditions, of the salt of an alkali metal ofthe ligand with a rare earth metal borohydride in a suitable solvent,such as an ether, for example diethyl ether or tetrahydrofuran, or anyother solvent known to those skilled in the art. After reaction, themetallocene is separated from the reaction by-products by techniquesknown to those skilled in the art, such as filtration or precipitationfrom a second solvent. In the end, the metallocene is dried and isolatedin the solid form.

Like any synthesis carried out in the presence of an organometalliccompound, the synthesis of the metallocene and that of the catalyticsystem take place under anhydrous conditions under an inert atmosphere.Typically, the reactions are carried out starting from anhydroussolvents and compounds under anhydrous nitrogen or argon.

The organomagnesium compound useful for the purposes of the invention isof formula MgR¹R², in which R¹ and R², which may be identical ordifferent, represent a carbon group. Carbon group is understood to meana group which contains one or more carbon atoms. Preferably, le and R²contain from 2 to 10 carbon atoms. More preferentially, R¹ and R² eachrepresent an alkyl. The organomagnesium compound is advantageously adialkylmagnesium compound, better still butylethylmagnesium orbutyloctylmagnesium, even better still butyloctylmagnesium.

According to any one of the embodiments of the invention, the molarratio of the organomagnesium compound to the metal Nd constituting themetallocene is preferably within a range extending from 1 to 100, morepreferentially is greater than or equal to 1 and less than 10. The rangeof values extending from 1 to less than 10 is in particular morefavourable for obtaining copolymers of high molar masses.

When the copolymer useful for the purposes of the invention is acopolymer which has a microstructure as defined according to the firstvariant of the invention, it is prepared according to the processmentioned in the present application using a metallocene of formula (II)in which Cp¹ and Cp², which may be identical or different, are selectedfrom the group consisting of substituted fluorenyl groups and theunsubstituted fluorenyl group of formula C₁₃H₈. For this variant, themetallocenes of the following formulae, in which the symbol Flu presentsthe fluorenyl group of formula C₁₃H₈, are particularly suitable:[{Me₂SiFlu₂Nd(μ-BH₄)₂Li(THF)}₂]; [Me₂SiFlu₂Nd(μ-BH₄)₂Li(THF)];[Me₂SiFlu₂Nd(μ-BH₄)(THF)]; [{Me₂SiFlu₂Nd(μ-BH₄)(THF)}₂];[Me₂SiFlu₂Nd(μ-BH₄)].

When the copolymer useful for the purposes of the invention is acopolymer which has a microstructure as defined according to the secondvariant of the invention, it is prepared according to the processmentioned in the present application using a metallocene of formula (II)in which Cp¹ denotes a cyclopentadienyl group Cp of formula C₅H₄ and Cp²denotes a fluorenyl group Flu of formula C₁₃H₈.

Those skilled in the art also know how to adjust the polymerizationconditions and the concentrations of each of the reactants (constituentsof the catalytic system, monomers) according to the equipment (devices,reactors) used to carry out the polymerization and the various chemicalreactions. As is known to those skilled in the art, the copolymerizationand the handling of the monomers, of the catalytic system and of thepolymerization solvent(s) take place under anhydrous conditions andunder an inert atmosphere. The polymerization solvents are typicallyaliphatic or aromatic hydrocarbon solvents.

The polymerization is preferably carried out in solution, continuouslyor batchwise. The polymerization solvent can be an aromatic or aliphatichydrocarbon solvent. Mention may be made, as examples of polymerizationsolvent, of toluene and methylcyclohexane. The monomers can beintroduced into the reactor containing the polymerization solvent andthe catalytic system or, conversely, the catalytic system can beintroduced into the reactor containing the polymerization solvent andthe monomers. The copolymerization is typically carried out underanhydrous conditions and in the absence of oxygen, in the optionalpresence of an inert gas. The polymerization temperature generallyvaries within a range extending from 30 to 150° C., preferentially from30 to 120° C. Preferably, the copolymerization is carried out atconstant ethylene pressure.

During the polymerization of ethylene and the 1,3-diene in apolymerization reactor, ethylene and 1,3-diene can be added continuouslyto the polymerization reactor, in which case the polymerization reactoris a fed reactor. This embodiment is very particularly suitable for thesynthesis of a random copolymer.

The polymerization can be halted by cooling the polymerization medium.The polymer can be recovered according to conventional techniques knownto those skilled in the art, such as, for example, by precipitation, byevaporation of the solvent under reduced pressure or by steam stripping.

Preferably, the rubber composition according to the invention comprisesfrom 15 to less than 50 phr, preferably from 20 to 45 phr, of acopolymer of ethylene and of a 1,3-diene of formula (I) as defined inany one of the embodiments described above, including variants thereof.It is understood that the copolymer may consist of a mixture ofcopolymers which differ from one another in their microstructure ortheir macrostructure.

According to the invention, the composition also comprises from 5 to 95phr of polyisoprene comprising a content by weight of 1,4-cis bonds ofat least 90% of the weight of the polyisoprene.

Advantageously, the polyisoprene is a polyisoprene comprising a contentby weight of 1,4-cis bonds of at least 98% of the weight of thepolyisoprene.

Preferably, the polyisoprene is selected from the group consisting ofnatural rubber, synthetic polyisoprenes, and mixtures thereof. Morepreferably, the polyisoprene is a natural rubber.

Advantageously, the content of the polyisoprene, preferably of naturalrubber, in the composition according to the invention is within a rangeextending from more than 50 to 85 phr, preferably from 55 to 80 phr.

II-2 Reinforcing Filler

The composition according to the invention may also comprise areinforcing filler. Such a reinforcing filler typically consists ofnanoparticles, the (weight-)average size of which is less than amicrometre, generally less than 500 nm, most often between 20 and 200nm, in particular and more preferentially between 20 and 150 nm.

The reinforcing filler can comprise carbon black, silica, or a mixturethereof. The composition of the first layer of the laminate according tothe invention can mainly consist of silica. Preferably, it can mainly,preferably exclusively, consist of carbon black. More preferably, thereinforcing filler consists of at least 80% by weight, preferably of atleast 90% by weight, of carbon black. Preferably, the reinforcing fillercomprises exclusively, that is to say 100% by weight, carbon black. Thecarbon black may be a mixture of different carbon blacks, in which casethe contents of carbon black relate to all of the carbon blacks.

All carbon blacks, in particular the blacks conventionally used in tyresor their treads, are suitable as carbon blacks. Among the latter,mention will more particularly be made of the reinforcing carbon blacksof the 100, 200 and 300 series, or the blacks of the 500, 600 or 700series (ASTM D-1765-2017 grades), such as, for example, the N115, N134,N234, N326, N330, N339, N347, N375, N550, N683 and N772 blacks. Thesecarbon blacks can be used in the isolated state, as availablecommercially, or in any other form, for example as support for some ofthe rubber additives used. The carbon blacks might, for example, bealready incorporated in the diene elastomer, in particular isopreneelastomer, in the form of a masterbatch (see, for example, applicationsWO97/36724-A2 and WO99/16600-A1).

The content of reinforcing filler is adjusted by those skilled in theart according to the use of the rubber composition. Advantageously, thecontent of reinforcing filler, preferably of carbon black, in thecomposition according to the invention, is within a range extending from15 to 80 phr, preferably from 20 to 55 phr, preferably from 25 to 45phr.

Also preferably, the volume fraction of reinforcing filler, preferablyof carbon black, in the composition according to the invention is withina range extending from 8% to 15%. In a known manner, the volume fractionof a constituent in a rubber composition is defined as being the ratioof the volume of this constituent to the volume of all the constituentsof the composition, it being understood that the volume of all theconstituents is calculated by adding together the volume of each of theconstituents of the composition. The volume fraction of carbon black ina composition is therefore defined as the ratio of the volume of carbonblack to the sum of the volumes of each of the constituents of thecomposition. The volume of a constituent is accessible through the ratiobetween the weight of the constituent introduced into the rubbercomposition and the density of the constituent. In a known manner, thevolume fraction of carbon black for a given content in phr of carbonblack can be adjusted by introducing a plasticizer into the composition.

Silicas that are suitable include any type of precipitated silica, inparticular highly dispersible precipitated silicas (referred to as “HDS”for “highly dispersible” or “highly dispersible silica”). Theseprecipitated silicas, which are or are not highly dispersible, are wellknown to those skilled in the art. Mention may be made, for example, ofthe silicas described in applications WO03/016215-A1 and WO03/016387-A1.Use may in particular be made, among commercial HDS silicas, of theUltrasil® 5000GR and Ultrasil® 7000GR silicas from Evonik or the Zeosil®1085GR, Zeosil® 1115 MP, Zeosil® 1165MP, Zeosil® Premium 200MP andZeosil® HRS 1200 MP silicas from Solvay. Use may be made, as non-HDSsilica, of the following commercial silicas: the Ultrasil® VN2GR andUltrasil® VN3GR silicas from Evonik, the Zeosil® 175GR silica fromSolvay or the Hi-Sil EZ120G(-D), Hi-Sil EZ160G(-D), Hi-Sil EZ200G(-D),Hi-Sil 243LD, Hi-Sil 210 and Hi-Sil HDP 320G silicas from PPG.

Use may be made, in order to couple the silica to the diene elastomer,in a well-known way, of an at least bifunctional coupling agent (orbonding agent) intended to provide a satisfactory connection, ofchemical and/or physical nature, between the inorganic filler (surfaceof its particles) and the diene elastomer. Use is made in particular oforganosilanes or polyorganosiloxanes which are at least bifunctional.The term “bifunctional” is understood to mean a compound having a firstfunctional group capable of interacting with the inorganic filler and asecond functional group capable of interacting with the diene elastomer.For example, such a bifunctional compound can comprise a firstfunctional group comprising a silicon atom, said first functional groupbeing capable of interacting with the hydroxyl groups of an inorganicfiller, and a second functional group comprising a sulfur atom, saidsecond functional group being capable of interacting with the dieneelastomer.

Preferably, the organosilanes are selected from the group consisting oforganosilane polysulfides (symmetrical or asymmetrical), such asbis(3-triethoxysilylpropyl) tetrasulfide, abbreviated to TESPT, soldunder the name Si69 by Evonik, or bis(3-triethoxysilylpropyl)disulfide,abbreviated to TESPD, sold under the name Si75 by Evonik,polyorganosiloxanes, mercaptosilanes, blocked mercaptosilanes, such asS-(3-(triethoxysilyl)propyl) octanethioate, sold by Momentive under thename NXT Silane. More preferentially, the organosilane is anorganosilane polysulfide.

When silica is used, the content of coupling agent in the composition ofthe first layer of the laminate of the invention can easily be adjustedby those skilled in the art. Typically, the content of coupling agentrepresents from 0.5% to 15% by weight, with respect to the amount ofsilica.

II-3 Crosslinking System

The crosslinking system can be any type of system known to those skilledin the art in the field of rubber compositions for tyres. It may inparticular be based on sulfur, and/or on peroxide and/or onbismaleimides.

Preferentially, the crosslinking system is based on sulfur; it is thencalled a vulcanization system. The sulfur can be contributed in anyform, in particular in the form of molecular sulfur or of asulfur-donating agent. At least one vulcanization accelerator is alsopreferentially present, and, optionally, also preferentially, use may bemade of various known vulcanization activators, such as zinc oxide,stearic acid or equivalent compound, such as stearic acid salts, andsalts of transition metals, guanidine derivatives (in particulardiphenylguanidine), or also known vulcanization retarders.

The sulfur is used at a preferential content of between 0.3 phr and 10phr, more preferentially between 0.3 and 5 phr. The primaryvulcanization accelerator is used at a preferential content of between0.5 and 10 phr, more preferentially of between 0.5 and 5 phr.

Use may be made, as accelerator, of any compound capable of acting asaccelerator of the vulcanization of diene elastomers in the presence ofsulfur, in particular accelerators of the thiazole type, and also theirderivatives, or accelerators of sulfenamide, thiuram, dithiocarbamate,dithiophosphate, thiourea and xanthate types. Mention may in particularbe made, as examples of such accelerators, of the following compounds:2-mercaptobenzothiazyl disulfide (abbreviated to “MBTS”),N-cyclohexyl-2-benzothiazolesulfenamide (“CBS”),N,N-dicyclohexyl-2-benzothiazolesulfenamide (“DCBS”),N-(tert-butyl)-2-benzothiazolesulfenamide (“TBBS”),N-(tert-butyl)-2-benzothiazolesulfenimide (“TBSI”), tetrabenzylthiuramdisulfide (“TBZTD”), zinc dibenzyldithiocarbamate (“ZBEC”) and themixtures of these compounds.

II-4 Possible Additives

The rubber composition which is useful for the purposes of the inventionmay also comprise all or some of the usual additives normally used inelastomer compositions intended for use in a tyre, such as, for example,processing agents, plasticizers, pigments, protective agents such asanti-ozone waxes, chemical anti-ozonants, antioxidants. Preferably, therubber composition comprises a plasticizer. Suitable plasticizers areall the plasticizers conventionally used in tyres. In this respect,mention may be made of oils which are preferentially non-aromatic orvery weakly aromatic, selected from the group consisting of naphthenicoils, paraffin oils, MES oils, TDAE oils, plant oils, etherplasticizers, ester plasticizers.

II-5 Preparation of the Rubber Compositions

The compositions in accordance with the invention can be manufactured inappropriate mixers using two successive preparation phases well known tothose skilled in the art:

-   -   a first phase of thermomechanical working or kneading        (“non-productive” phase), which can be carried out in a single        thermomechanical step during which all the necessary        constituents, in particular the elastomeric matrix, the        reinforcing filler and the optional other various additives,        with the exception of the crosslinking system, are introduced        into an appropriate mixer, such as a standard internal mixer        (for example of ‘Banbury’ type). The incorporation of the        optional filler into the elastomer can be carried out in one or        more goes by thermomechanically kneading. In the case where the        filler is already incorporated, in full or in part, in the        elastomer in the form of a masterbatch, as is described, for        example, in applications WO 97/36724 and WO 99/16600, it is the        masterbatch which is directly kneaded and, if appropriate, the        other elastomers or fillers present in the composition which are        not in the masterbatch form, and also the optional other various        additives other than the crosslinking system, are incorporated.        The non-productive phase can be carried out at high temperature,        up to a maximum temperature of between 110° C. and 200° C.,        preferably between 130° C. and 185° C., for a period of time        generally of between 2 and 10 minutes.    -   a second phase of mechanical working (“productive” phase), which        is carried out in an external mixer, such as an open mill, after        cooling the mixture obtained during the first non-productive        phase down to a lower temperature, typically of less than 120°        C., for example between 40° C. and 100° C. The crosslinking        system is then incorporated and the combined mixture is then        mixed for a few minutes, for example between 5 and 15 min.

Such phases have been described, for example, in applicationsEP-A-0501227, EP-A-0735088, EP-A-0810258, WO 00/05300 or WO 00/05301.

The final composition thus obtained is then calendered, for example inthe form of a sheet or of a slab, in particular for characterization inthe laboratory, or else extruded (or co-extruded with another rubbercomposition) in the form of a semi-finished (or profiled) element ofrubber that can be used for example as a tyre sidewall. These productscan then be used for the manufacture of tyres, according to thetechniques known to those skilled in the art.

The composition may be either in the uncured state (before crosslinkingor vulcanization) or in the cured state (after crosslinking orvulcanization), may be a semi-finished product that can be used in atyre.

The crosslinking (or curing), where appropriate the vulcanization, iscarried out in a known manner at a temperature generally of between 130°C. and 200° C., for a sufficient time which may vary, for example,between 5 and 90 min, depending especially on the curing temperature, onthe crosslinking system adopted and on the crosslinking kinetics of thecomposition in question.

II-6 Tyre

Another subject of the present invention is a tyre comprising a rubbercomposition according to the invention.

Preferably, the composition according to the invention is present atleast in a sidewall of the tyre according to the invention.Advantageously, this composition is present exclusively in the sidewallsof the tyre.

The tyre according to the invention can be intended to equip motorvehicles of private passenger type, SUVs (sport utility vehicles), ortwo-wheeled vehicles (in particular motorbikes), or aeroplanes, or elseindustrial vehicles chosen from vans, heavy-goods vehicles—that is tosay underground trains, buses, road haulage vehicles (lorries, tractors,trailers), off-road vehicles such as agricultural vehicles or civilengineering plant—and more.

III—PREFERRED EMBODIMENTS

In the light of the above, the preferred embodiments of the inventionare described below:

-   A. Rubber composition at least based on:    -   5 to 95 phr of polyisoprene comprising a content by weight of        1,4-cis bonds of at least 90% of the weight of the polyisoprene,    -   5 to 95 phr of copolymer of ethylene and of a 1,3-diene of        formula (I), the ethylene units in the copolymer representing        more than 50 mol % of the monomer units of the copolymer,

CH₂═CR—CH═CH₂  (I)

the symbol R representing a hydrocarbon chain having 3 to 20 carbonatoms, and

-   -   a crosslinking system.

-   B. Rubber composition according to embodiment A, wherein the    copolymer contains ethylene units which represent between 50 mol %    and 95 mol %, preferably from 60 mol % to 90 mol %, more preferably    from 70 mol % to 85 mol %, of the monomer units of the copolymer.

-   C. Rubber composition according to any one of the preceding    embodiments, wherein the copolymer contains units of the 1,3-diene    of 1,2 or 3,4 configuration which represent more than 50 mol % of    the units of the 1,3-diene.

-   D. Rubber composition according to any one of the preceding    embodiments, wherein the symbol R represents a hydrocarbon chain    having 6 to 16 carbon atoms.

-   E. Rubber composition according to any one of the preceding    embodiments, wherein the symbol R represents an aliphatic chain.

-   F. Rubber composition according to any one of the preceding    embodiments, wherein the symbol R represents an acyclic chain.

-   G. Rubber composition according to any of the preceding embodiments,    wherein the symbol R represents a linear or branched chain.

-   H. Rubber composition according to any one of the preceding    embodiments, wherein the 1,3-diene is myrcene or β-farnesene.

-   I. Rubber composition according to any one of the preceding    embodiments, wherein the copolymer has a glass transition    temperature below −35° C., preferably between −90° C. and −35° C.

-   J. Rubber composition according to any one of the preceding    embodiments, wherein the content of the copolymer is within a range    extending from from 15 to less than 50 phr.

-   K. Rubber composition according to any one of the preceding    embodiments, wherein the polyisoprene comprises a content by weight    of 1,4-cis bonds of at least 98% of the weight of the polyisoprene.

-   L. Rubber composition according to any one of the preceding    embodiments, wherein the polyisoprene is selected from the group    consisting of natural rubber, synthetic polyisoprenes and mixtures    thereof; preferably the polyisoprene is a natural rubber.

-   M. Rubber composition according to any one of the preceding    embodiments, wherein the copolymer has a glass transition    temperature below −35° C., preferably between −90° C. and −35° C.

-   N. Rubber composition according to any one of the preceding    embodiments, also comprising a reinforcing filler.

-   O. Rubber composition according to embodiment N, wherein the    reinforcing filler comprises mainly carbon black.

-   P Rubber composition according to embodiment N, wherein the    reinforcing filler comprises mainly silica.

-   Q. Rubber composition according to any one of the preceding    embodiments, wherein the content of reinforcing filler is within a    range extending from 15 to 80 phr, preferably from 20 to 55 phr,    preferably from 25 to 45 phr.

-   R. Rubber composition according to any one of the preceding    embodiments, wherein the volume fraction of the reinforcing filler,    preferably of the carbon black, is within a range extending from 8%    to 17%, preferably from 8% to 15%.

-   S. Rubber composition according to any one of embodiments A to 0, Q    and R, wherein the content of the polyisoprene is within a range    extending from more than 50 to 85 phr, the content of the copolymer    is within a range extending from 15 to less than 50 phr, and    comprising a reinforcing filler comprising mainly carbon black.

-   T. Tyre comprising a rubber composition defined in any one of    embodiments A to S.

-   U. Tyre according to embodiment T, wherein the rubber composition    defined in any one of embodiments A to S is present in at least one    sidewall of the tyre.

IV—EXAMPLES

IV-1 Measurements and Tests Used

IV-1.1 Determination of the Microstructure of the Elastomers:

The spectral characterization and the measurements of the microstructureof the copolymers of ethylene and of 1,3-myrcene are carried out bynuclear magnetic resonance (NMR) spectroscopy.

Spectrometer: For these measurements, a Bruker Avance III HD 400 MHzspectrometer is used, equipped with a Bruker cryo-BBFO z-grad 5 mmprobe.

Experiments: The ¹H experiments are recorded using a radiofrequencypulse with a tilt angle of 30°, the number of repetitions is 128 with arecycle delay of 5 seconds. The HSQC (Heteronuclear Single QuantumCoherence) and HMBC (Heteronuclear Multiple-Bond Correlation)¹H-¹³C NMRcorrelation experiments are recorded with a number of repetitions of 128and a number of increments of 128. The experiments are carried out at25° C.

Preparation of the sample: 25 mg of sample are dissolved in 1 ml ofdeuterated chloroform (CDCl₃).

Sample calibration: The axes of the ¹H and ¹³C chemical shifts arecalibrated with respect to the protonated impurity of the solvent(CHCl₃) at δ_(1H)=7.2 ppm and δ_(13C)=⁷⁷ ppm.

Spectral assignment for the copolymers of ethylene and of 1,3-myrcene:In the representations A, B and C below, the symbols R1 and R2 representthe attachment points of the unit to the polymer chain. The signals ofthe insertion forms of the 1,3-diene A, B and C were observed on thedifferent spectra recorded. According to S. George et al., (Polymer 55(2014) 3869-3878), the signal of the —CH═group No. 8″ characteristic ofform C exhibits ¹H and ¹³C chemical shifts identical to the —CH═groupNo. 3. The chemical shifts of the signals characteristic of the moietiesA, B and C are presented in Table 1. The moieties A, B and C correspondrespectively to the units of 3,4 configuration, of 1,2 configuration andof trans-1,4 configuration. The quantifications were carried out fromthe integration of the 1D ¹H NMR spectra using the Topspin software. Theintegrated signals for the quantification of the various moieties are:

Ethylene: signal at 1.2 ppm corresponding to 4 protonsTotal myrcene: signal No. 1 (1.59 ppm) corresponding to 6 protonsForm A: signal No. 7 (4.67 ppm) corresponding to 2 protonsForm B: signal No. 8′ (5.54 ppm) corresponding to 1 proton.

The quantification of the microstructure is carried out in molarpercentage (molar %) as follows: Molar % of a moiety=¹H integral of amoiety×100/Σ(¹H integrals of each moiety).

TABLE 1 Assignment of the ¹H and ¹³C signals of Ethylene-Myrcenecopolymers δ_(1H) (ppm) δ_(13C) (ppm) Group 5.54 146.4 8′ 5.07 124.6 3 +8″ 4.97-4.79 112.0 9′ 4.67 108.5 7  2.06  26.5 4   2.0-1.79  31.8 5 +5′ + 5″  44.5 8  1.59 25.9 and 7.0 1  1.2  36.8-24.0 CH₂ ethylene

IV-1.2 Determination of the Glass Transition Temperature of thePolymers:

The glass transition temperature is measured by means of a differentialcalorimeter (differential scanning calorimeter) according to StandardASTM D3418 (1999).

IV-2 Synthesis of the Polymers:

In the synthesis of copolymers in accordance with the invention, the1,3-diene used is myrcene, a 1,3-diene of formula (I) in which R is ahydrocarbon group having 6 carbon atoms: CH₂—CH₂—CH═CMe₂.

All the reagents are obtained commercially, except the metallocenes.[{Me₂SiFlu₂Nd(μ-BH₄)₂Li(THF)}] is prepared according to the proceduredescribed in patent application WO 2007/054224.

The butyloctylmagnesium BOMAG (20% in heptane, C=0.88 mol.l⁻¹)originates from Chemtura and is stored in a Schlenk tube under an inertatmosphere. The ethylene, of N35 grade, originates from Air Liquide andis used without prepurification. The myrcene (purity≥95%) is obtainedfrom Sigma-Aldrich.

IV-2.1—Copolymer of Ethylene and of 1,3-Butadiene: Elastomer E1

To a reactor containing, at 80° C., methylcyclohexane, ethylene (Et) andbutadiene (Bd) in the proportions indicated in Table 2,butyloctylmagnesium (BOMAG) is added to neutralize the impurities in thereactor, then the catalytic system is added (see Table 2). At this time,the reaction temperature is regulated at 80° C. and the polymerizationreaction starts. The polymerization reaction takes place at a constantpressure of 8 bar. The reactor is fed throughout the polymerization withethylene and butadiene in the proportions defined in Table 2. Thepolymerization reaction is halted by cooling, degassing of the reactorand addition of ethanol. An antioxidant is added to the polymersolution. The copolymer is recovered by drying in an oven under vacuumto constant weight. The catalytic system is a preformed catalyticsystem. It is prepared in methylcyclohexane from a metallocene,[Me₂SiFlu₂Nd(μ-BH₄)₂Li(THF)], a co-catalyst, butyloctylmagnesium(BOMAG), and a preformation monomer, 1,3-butadiene, in the contentsindicated in Table 2. It is prepared according to a preparation methodin accordance with paragraph II.1 of patent application WO 2017/093654.

IV-2.2—Copolymer of Ethylene and of Myrcene: Elastomer E2

To a reactor containing, at 80° C., methylcyclohexane, ethylene andmyrcene (My) in the proportions indicated in Table 2,butyloctylmagnesium (BOMAG) is added to neutralize the impurities in thereactor, then the catalytic system is added (see Table 2). At this time,the reaction temperature is regulated at 80° C. and the polymerizationreaction starts. The polymerization reaction takes place at a constantpressure of 8 bar. The reactor is fed throughout the polymerization withethylene and myrcene in the proportions defined in Table 2. Thepolymerization reaction is halted by cooling, degassing of the reactorand addition of ethanol. An antioxidant is added to the polymersolution. The copolymer is recovered by drying in an oven under vacuumto constant weight. The catalytic system is a preformed catalyticsystem. It is prepared in methylcyclohexane from a metallocene,[Me₂SiFlu₂Nd(μ-BH₄)₂Li(THF)], a co-catalyst, butyloctylmagnesium(BOMAG), and a preformation monomer, 1,3-butadiene, in the contentsindicated in Table 2. It is prepared according to a preparation methodin accordance with paragraph II.1 of patent application WO 2017/093654.

The microstructure of the polymers and the properties thereof are shownin Tables 3 and 4.

TABLE 2 Synthesis E1 E2 Metallocene concentration  0.07  0.039 (mmol/l)Alkylant agent concentration  0.36  0.2   (mmol/l) Preformation monomer/90    90     Nd metal molar ratio Composition of the feed 80/20 — (mol %Et/Bd) Composition of the feed — 65/35 (mol % Et/My)

TABLE 3 Elastomer E1 E2 Et (mol %) 78 76 Bd (mol %) 141,2-Cyclohexanediyl (mol %)  8 My (mol %) — 24 1,4 Myrcene (mol %/mol %My) — 29 1,2 Myrcene (mol %/mol % My) —  4 3,4 Myrcene (mol %/mol % My)— 67

TABLE 4 Elastomer Tg (° C.) E1 −40 E2 −63

IV-3 Preparation of the Rubber Compositions:

In the examples which follow, the rubber compositions were produced asdescribed in point II-5 above. In particular, the “non-productive” phasewas carried out in a 3 litre mixer for 5 minutes, for a mean blade speedof 50 revolutions per minute, until a maximum dropping temperature of160° C. was reached. The “productive” phase was carried out in an openmill at 23° C. for 10 minutes.

IV-4 Rubber Tests:

The adhesion of several rubber compositions comprising a mixture ofnatural rubber and copolymer of ethylene and of 1,3-diene on acomposition based on natural rubber was compared according to the natureand the content of the copolymer of ethylene and of 1,3-diene.

The adhesion measurements were carried out using a T-type peel test,also referred to as 180° peeling. The peeling test specimens areproduced by bringing into contact the two layers (the compositionsconstituting the layers being in the uncured state) for which theadhesion is to be tested. An incipient crack was inserted between thetwo layers. Each of the layers was reinforced by a composite ply whichlimits the deformation of said layers under traction.

The test specimen, once assembled, was brought to 150° C. under apressure of 16 bar, for 30 minutes. Strips with a width of 30 mm werethen cut out using a cutting machine. The two sides of the incipientcrack were subsequently placed in the jaws of an Instron brand tensiletesting machine. The tests were carried out at 20° C. and at a pullspeed of 100 mm/min. The tensile stresses were recorded and the latterwere standardized by the width of the test specimen. A curve of strengthper unit of width (in N/mm) as a function of the movable crossheaddisplacement of the tensile testing machine (between 0 and 200 mm) wasobtained. The adhesion value selected corresponds to the propagation ofthe crack within the test specimen and thus to the mean stabilized valueof the curve. The adhesion values of the examples were standardizedrelative to a control (base 100). An index of greater than 100 indicatesa greater improvement in adhesion.

The adhesion of compositions C1 to C6, in accordance with the invention,was compared with controls T1 to T6 not in accordance with the inventionwhich differ respectively from compositions C1 to C6 only by the natureof the 1,3-diene: 1,3 diene of formula (I) for compositions C1 to C6 and1,3-butadiene for compositions T1 to T6 (the elastomers E1 and E2 wereprepared according to the process described in point IV.2 above).

The layer based on natural rubber on which the adhesion was testedcorresponds to a composition conventionally used in the inner layer of atyre, such as a carcass ply or a tread underlayer, comprising 100 phr ofnatural rubber.

The compositions tested (in phr), as well as the results obtained, arepresented in Table 5.

TABLE 5 Compositions T1 C1 T2 C2 T3 C3 T4 C4 T5 C5 T6 C6 NR(1) 60 60 8080 20 20 40 40 60 60 80 80 Elastomer E1 40 — 20 — 80 — 60 — 40 — 20 —Elastomer E2 — 40 — 20 — 80 — 60 — 40 — 20 N234(2) 40 40 40 40 — — — — —— — — Silica(3) — — — — 48 48 48 48 48 48 48 48 Coupling — — — — 3.8 3.83.8 3.8 3.8 3.8 3.8 3.8 agent(4) DPG(5) — — — — 1 1 1 1 1 1 1 1Antioxidant(6) 2 2 2 2 2 2 2 2 2 2 2 2 Anti-ozone 1 1 1 1 1 1 1 1 1 1 11 wax(7) Stearic acid 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5ZnO(8) 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Accelerator(9)1.3 1.3 1.3 1.3 1.3 1.3 1.3 1.3 1.3 1.3 1.3 1.3 Sulfur 0.6 0.6 0.6 0.60.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 Adhesion 100 263 100 142 100 152 100 164100 206 100 109 (1)NR: Natural rubber (2)Carbon black N234 according toStandard ASTM D-1765-2017 (3)Silica, Zeosil 1165MP, sold by Solvay(4)Liquid silane triethoxysilylpropyltetrasulfide (TESPT) Si69 fromEvonik (5)Diphenylguanidine, Perkacit DPG from Flexsys(6)N-(1,3-Dimethylbutyl)-N-phenyl-para-phenylenediamine Santoflex 6-PPDfrom Flexsys (7)Anti-ozone wax, Varazon 4959 from Sasol Wax (8)Zincoxide, industrial grade from Umicore(9)N-Cyclohexyl-2-benzothiazolesulphenamide Santocure CBS from Flexsys

These results show that the use of a rubber composition in accordancewith the invention comprising a copolymer of ethylene and of 1,3-dieneof formula (I) makes it possible to improve the adhesion on a dienecomposition compared to a rubber composition not in accordance with theinvention comprising a copolymer of ethylene and of 1,3-diene.

1.-15. (canceled)
 16. A rubber composition at least based on: 5 to 95phr of polyisoprene comprising a content by weight of 1,4-cis bonds ofat least 90% of the weight of the polyisoprene; 5 to 95 phr of copolymerof ethylene and of a 1,3-diene of formula (I), the ethylene units in thecopolymer representing more than 50 mol % of the monomer units of thecopolymer,CH₂═CR—CH═CH₂  (I), the symbol R representing a hydrocarbon chain having3 to 20 carbon atoms; and a crosslinking system.
 17. The rubbercomposition according to claim 16, wherein the copolymer containsethylene units which represent between 50 mol % and 95 mol % of themonomer units of the copolymer.
 18. The rubber composition according toclaim 16, wherein the copolymer contains units of the 1,3-diene of 1,2or 3,4 configuration which represent more than 50 mol % of the units ofthe 1,3-diene.
 19. The rubber composition according to claim 16, wherein1,3-diene is myrcene or β-farnesene.
 20. The rubber compositionaccording to claim 16, wherein the copolymer has a glass transitiontemperature below −35° C.
 21. The rubber composition according to claim16, wherein a content of the copolymer is within a range extending from15 to less than 50 phr.
 22. The rubber composition according to claim16, wherein the polyisoprene comprises a content by weight of 1,4-cisbonds of at least 98% of the weight of the polyisoprene.
 23. The rubbercomposition according to claim 16, wherein the polyisoprene is selectedfrom the group consisting of natural rubber, synthetic polyisoprenes andmixtures thereof.
 24. The rubber composition according to claim 16,wherein the copolymer has a glass transition temperature between −90° C.and −35° C.
 25. The rubber composition according to claim 16, furthercomprising a reinforcing filler.
 26. The rubber composition according toclaim 25, wherein the reinforcing filler comprises mainly carbon black.27. The rubber composition according to claim 25, wherein a content ofreinforcing filler is within a range extending from 15 to 80 phr. 28.The rubber composition according to claim 16, wherein a content of thepolyisoprene is within a range extending from more than 50 to 85 phr,and a content of the copolymer is within a range extending from 15 toless than 50 phr, and further comprising a reinforcing filler comprisingmainly carbon black.
 29. A tire comprising the rubber compositionaccording to claim
 16. 30. The tire according to claim 29, wherein therubber composition is present in at least one sidewall of the tire.